Antenna and wireless ic device

ABSTRACT

An antenna and a wireless IC device that includes the antenna are provided for which the manufacturing process is simple and for which there is a low probability of a poor connection occurring between a feeder portion and a radiation electrode. An antenna includes a radiation electrode that is provided on a main surface of an insulator board, a ground electrode and/or a counter electrode that is arranged so as to oppose the radiation electrode, and a magnetic field electrode that is connected to the radiation electrode through a connection portion. The magnetic field electrode is defined by line-shaped electrodes and feeds a signal to the radiation electrode from a feeder portion defined by ends of the line-shaped electrodes through the magnetic field electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication apparatuses and,in particular, to antennas and wireless IC devices used in radiofrequency identification (RFID) systems.

2. Description of the Related Art

In recent years, as article management systems, RFID systems have beendeveloped in which communication is performed by using a non-contactmethod in which an electromagnetic field is utilized to transmitpredetermined information between a reader/writer, which generates aninduction field, and an IC tag (hereafter referred to as a wireless ICdevice), which is attached to an article and stores predeterminedinformation therein.

A known wireless IC device used in such an RFID system includes awireless IC chip that processes predetermined radio signals and aradiation electrode pattern that transmits and receives radio signals,and is disclosed, for example, in International Unexamined PublicationNo. WO2007/083574. International Unexamined Publication No.WO2007/083574 discloses an example of a radiation electrode pattern thatincludes a patch electrode.

However, there is a problem with radiation electrodes that include apatch electrode in that, for example, it is necessary to provide afeeder pin arranged to feed a signal to the patch electrode inside aninsulating board and to provide a feeder electrode on a side surface ofthe board. The formation of such a feeder portion is difficult, themanufacturing process is complicated, and a poor connection with theradiation electrode occurs at an edge portion of the insulating board.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide an antenna and a wireless IC device thatincludes the antenna for which the manufacturing process is simple andin which a poor connection occurring between a feeder portion and aradiation electrode is prevented.

An antenna according to a first preferred embodiment of the presentinvention preferably includes a radiation electrode that is provided onone main surface of an insulator board, a magnetic field electrode thatis connected to the radiation electrode, and a feeder portion that isconnected to the magnetic field electrode, the radiation electrode beingarranged in an area surrounding the magnetic field electrode.

An antenna according to a second preferred embodiment of the presentinvention preferably includes a radiation electrode that is provided onone main surface of an insulator board, a ground electrode that isarranged on another main surface of the insulator board so as to opposethe radiation electrode, a magnetic field electrode that is connected tothe radiation electrode, and a feeder portion that is connected to themagnetic field electrode.

An antenna according to a third preferred embodiment of the presentinvention preferably includes a radiation electrode that is provided onone main surface of an insulator board, a counter electrode that isarranged on another main surface of the insulator board so as to opposethe radiation electrode and that is coupled with the radiation electrodethrough a capacitance, a magnetic field electrode that is connected tothe radiation electrode, and a feeder portion that is connected to themagnetic field electrode. This antenna may preferably further include aground electrode that is arranged so as to oppose the counter electrode.

Each of the antennas according to the first, second and third preferredembodiments preferably includes a magnetic field electrode that isdisposed between the radiation electrode and the feeder portion andfunctions as an antenna. With this structure, the feeder pin and sidesurface electrode, which were necessary in patch antennas of thebackground art, are no longer necessary, the process of manufacturingthe antenna is simplified, and the reliability of a connection betweenthe radiation electrode and the feeder portion is improved.

A wireless IC device according to a fourth preferred embodiment of thepresent invention preferably includes the antenna and a wireless IC, thewireless IC being arranged so as to be coupled with a feeder portion.With this structure, a wireless IC device can be manufactured that has asmall size and for which the manufacturing method is simple.

A wireless IC device according to a fifth preferred embodiment of thepresent invention preferably includes an antenna, a wireless IC, and anelectromagnetic coupling module that is coupled with the wireless IC andis disposed on a feeder circuit board, the feeder circuit boardpreferably including a feeder circuit that is defined by a resonancecircuit and/or a matching circuit that includes an inductance element,and the electromagnetic coupling module being arranged so as to becoupled with a feeder portion. With this structure, impedance matchingcan be performed between the antenna and the wireless IC in the feedercircuit board, a region that defines a matching circuit between theradiation electrode and the wireless IC that was necessary in thebackground art can be omitted, and the wireless IC device can be reducedin size.

According to preferred embodiments of the present invention, a radiationelectrode and a feeder portion are preferably connected to each otherthrough a magnetic field electrode (magnetic field antenna) and,therefore, a connection portion that has a complex structure and thatwas necessary in the background art can be omitted, the process ofmanufacturing the antenna is simplified, and the occurrence of a poorconnection between the feeder portion and the radiation electrode isminimized or prevented.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B illustrate an antenna according to a first preferredembodiment of the present invention, where FIG. 1A is an explodedperspective view and FIG. 1B is a sectional view along line A-A of FIG.1A.

FIG. 2 is a perspective view illustrating operation of the antennaaccording to the first preferred embodiment of the present invention.

FIG. 3 is an enlarged view illustrating a coupling portion of theantenna according to the first preferred embodiment of the presentinvention.

FIG. 4 is an equivalent circuit diagram of a wireless IC device thatincludes the antenna according to the first preferred embodiment of thepresent invention.

FIG. 5 is an exploded perspective view illustrating an antenna accordingto a second preferred embodiment of the present invention.

FIG. 6 is an enlarged view illustrating a coupling portion of theantenna according to the second preferred embodiment of the presentinvention.

FIG. 7 is an exploded perspective view illustrating an antenna accordingto a third preferred embodiment of the present invention.

FIG. 8 is an equivalent circuit diagram of a wireless IC device thatincludes the antenna according to the third preferred embodiment of thepresent invention.

FIGS. 9A and 9B illustrate a wireless IC device according to a fourthpreferred embodiment of the present invention, where FIG. 9A is anexploded perspective view and FIG. 9B is a sectional view along line B-Bof FIG. 9A.

FIGS. 10A and 10B illustrate a feeder portion of the wireless IC deviceaccording to the fourth preferred embodiment of the present invention,where FIG. 10A is an enlarged view illustrating the arrangement ofterminal electrodes of the feeder portion and FIG. 10B is an enlargedview illustrating a state in which a wireless IC chip has been mountedon the feeder portion.

FIG. 11 is a perspective view of the wireless IC chip that is includedin the wireless IC device according to the fourth preferred embodimentof the present invention.

FIGS. 12A and 12B illustrate a wireless IC device according to a fifthpreferred embodiment of the present invention, where FIG. 12A is anexploded perspective view and FIG. 12B is a sectional view along lineC-C of FIG. 12A.

FIG. 13 is an equivalent circuit diagram illustrating a feeder circuitof the wireless IC device according to the fifth preferred embodiment ofthe present invention.

FIG. 14 is a perspective view illustrating a state in which a wirelessIC chip has been mounted on a feeder circuit board, the feeder circuitboard being included in the wireless IC device according to the fifthpreferred embodiment of the present invention.

FIG. 15 is a plan view illustrating the layered structure of the feedercircuit board included in the wireless IC device according to the fifthpreferred embodiment of the present invention of the present invention.

FIGS. 16A to 16C illustrate an antenna according to a sixth preferredembodiment of the present invention, where FIG. 16A is a plan view, FIG.16B is a perspective view of the antenna, and FIG. 16C is a perspectiveview of a state in which the antenna has been mounted on a metal plate.

FIG. 17 is a perspective view illustrating an antenna according to aseventh preferred embodiment of the present invention.

FIGS. 18A to 18D are plan views illustrating first, second, third andfourth modifications of the sixth preferred embodiment of the presentinvention.

FIGS. 19A and 19B illustrate an antenna according to an eighth preferredembodiment of the present invention, where FIG. 19A is a perspectiveview of the antenna and FIG. 19B is an equivalent circuit diagram of awireless IC device that includes the antenna.

FIGS. 20A and 20B illustrate an antenna according to a ninth preferredembodiment of the present invention, where FIG. 20A is a perspectiveview of the antenna and FIG. 20B is an equivalent circuit diagram of awireless IC device that includes the antenna.

FIGS. 21A and 21B illustrate an antenna according to a tenth preferredembodiment of the present invention, where FIG. 21A is a perspectiveview of the antenna and FIG. 21B is an equivalent circuit diagram of awireless IC device that includes the antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, antennas and wireless IC devices according to preferredembodiments of the present invention will be described with reference tothe accompanying drawings. In each of the drawings, common componentsand parts are denoted by the same symbols and repeated descriptionthereof is omitted.

First Preferred Embodiment

An antenna 20 according to a first preferred embodiment of the presentinvention is illustrated in FIGS. 1A and 1B. The antenna 20 preferablyincludes a radiation electrode 2 that is disposed on one main surface 11of an insulator board and has an opening 3 therein, a magnetic fieldelectrode 7 including a first line-shaped electrode 5 and a secondline-shaped electrode 6, which are connected to an inner peripheralportion of the opening 3 of the radiation electrode 2, and a feederportion 10 formed by arranging an end 8 of the first line-shapedelectrode 5 and an end 9 of the second line-shaped electrode 6 so as toface each other. In addition, insulator material 16 is preferablyarranged so as to cover the radiation electrode 2 on the one mainsurface 11 side of the insulator board 1. Furthermore, through holes 15are preferably screw holes, for example, with which the antenna 20 isscrewed onto a predetermined article, such as a metal plate, forexample. Instead of being fixed with screws, double-sided tape or aninsulating or conductive adhesive may be used to provide the connection.

The radiation electrode 2 functions as the radiation electrode of apatch antenna and is preferably arranged so as to provide wide portionson both sides of the insulator board 1 in the longitudinal directionthereof. The insulator board 1, which is provided with the radiationelectrode 2 and the magnetic field electrode 7, can preferably be formedby, for example, etching a metal foil preferably composed of Cu, Al orother suitable material formed on a surface of a resin board, such as aglass epoxy board, for example. The antenna 20 can preferably be formedby applying the insulator material 16, which is, for example, aninsulating resin, onto the one main surface 11 on which the radiationelectrode 2 has been formed. In addition, the antenna 20 may preferablybe formed in an integrated manner by performing injection molding of aresin, such as polyetherimide, for example, onto a metal pattern formedby punching a metal foil composed of Cu, Al or other suitable material.Furthermore, the antenna 20 according to this preferred embodimentpreferably has a size of about 68 mm in the longitudinal direction,about 40 mm in the width direction, and a thickness of about 3 mm, forexample. The thickness of the insulator material 16 is preferably about200 μm, for example.

Each of the first line-shaped electrode 5 and the second line-shapedelectrode 6 preferably includes a portion having a meandering shape, areconnected to each other in the vicinity of the radiation electrode 2,define the magnetic field electrode 7, and are connected to theradiation electrode 2 through a connection portion 13. In addition, thefirst line-shaped electrode 5 and the second line-shaped electrode 6 arenot limited to having a meandering shape and may be modified so as tohave any of a variety of suitable shapes so as to obtain desiredcharacteristics.

The operation of the antenna 20 according to the first preferredembodiment will now be described. First, at the time of transmission,when a signal is supplied from the feeder portion 10, a current flowsthrough the first line-shaped electrode 5 and the second line-shapedelectrode 6, which define the magnetic field electrode 7, due to thissignal. The first line-shaped electrode 5 and the second line-shapedelectrode 6 each have a predetermined length and, therefore, a potentialdifference is generated from the feeder portion 10 to the connectionportion 13. When the antenna 20 has been attached to, for example, ametal article (indicated by the symbol 42 in the equivalent circuit ofFIG. 4), the metal article 42 is coupled with the radiation electrode 2through a capacitance C1 and functions as a ground electrode.Furthermore, the magnetic field electrode 7 has a potential differencewith the metal article, which functions as a ground electrode, due tothe potential difference generated in the first line-shaped electrode 5and the second line-shaped electrode 6, and the radiation electrode 2,which is conductively connected to the first line-shaped electrode 5 andthe second line-shaped electrode 6, also has a potential difference withthe metal article. Due to the potential difference between the radiationelectrode 2 and the metal article (ground electrode), the radiationelectrode 2 operates as a patch antenna and a signal can be radiatedfrom the radiation electrode 2 to the outside.

Furthermore, at the time of reception, a signal transmitted from outsidethe antenna 20 is received by the magnetic field electrode 7. At thistime, a signal is received as a result of the magnetic field electrode 7becoming coupled with the magnetic field of a signal propagating throughspace and, thereby, a current is generated in the magnetic fieldelectrode 7 due to this received magnetic field. Due to this current, apotential difference is generated between the connection portion of thefirst line-shaped electrode 5 and the second line-shaped electrode 6,and the feeder portion 10. Due to this potential difference, similarlyto during transmission, the magnetic field electrode 7 has a potentialdifference with the metal article to which the antenna 20 has beenattached. Furthermore, the same potential difference is also generatedat the radiation electrode 2, which is conductively connected to themagnetic field electrode 7, and the radiation electrode 2 operates as apatch antenna and a signal can be received from the outside through theradiation electrode 2.

In addition, in the patch antenna of the first preferred embodiment,since the radiation electrode 2 has a closed loop shape, when a signalhaving a high frequency of several hundred MHz to several GHz istransmitted or received, the current is concentrated in an outerperipheral edge portion of the radiation electrode 2 due to the edgeeffect as indicated by the arrows in FIG. 2. Accordingly, even whensubstantially no current flows in the vicinity of the center of theradiation electrode 2 and the opening 3 is provided in the vicinity ofthe center of the radiation electrode 2, there is substantially noeffect on the frequency characteristics of the patch antenna. With thisstructure, the feeder portion 10 and the magnetic field electrode 7 canpreferably be arranged inside the opening 3 and the patch antenna can bereduced in size. Furthermore, as a result of the feeder portion 10 andthe radiation electrode 2 being connected to each other through themagnetic field electrode 7, the feeder portion 10 and the radiationelectrode 2 can preferably be arranged on the same surface of theinsulator board 1. Thus, a feeder pin and an electrode on the sidesurface of the board, which connect the feeder portion and the radiationelectrode and have been necessary to date, are no longer required, theprocess of manufacturing the antenna is simplified and the reliabilityof the connection between the feeder portion and the radiation electrodeis significantly improved.

In addition, the degree of coupling between the magnetic field electrode7 and the radiation electrode 2 can be adjusted by changing the width Wof the connection portion 13 and the separation L of the magnetic fieldelectrode 7 (line-shaped electrodes 5 and 6) and the radiation electrode2 illustrated in FIG. 3. As the width W of the connection portion andthe separation L increases, the degree of coupling decreases, and as thewidth W of the connection portion 13 and the separation L decreases, thedegree of coupling increases.

An equivalent circuit of the antenna 20 is illustrated in FIG. 4. InFIG. 4, an equivalent circuit is illustrated of a wireless IC device inwhich a wireless IC chip 51 (refer to FIG. 11), to be described below,is connected to the feeder portion 10 defined by the ends 8 and 9. Inaddition, in the antenna 20, a ground electrode (metal article 42)arranged so as to oppose the radiation electrode 2 is not necessarilyrequired. Even when a ground electrode (metal article 42) is notprovided, the radiation electrode 2 operates as an antenna (loop antennaor folded dipole antenna) due to the potential difference generated inthe magnetic field electrode 7.

Second Preferred Embodiment

An antenna 30 according to a second preferred embodiment of the presentinvention is illustrated in FIG. 5. The antenna 30 differs from theantenna 20 according to the first preferred embodiment in that thestructure of the connection portion 13 and the shape of the radiationelectrode 2 are different and in that a first connection portion 31 anda second connection portion 33 preferably are provided. In the antenna30, the magnetic field electrode 7 is preferably defined by the firstline-shaped electrode 5 and the second line-shaped electrode 6. Byarranging the connection portions 31 and 33 of the magnetic fieldelectrode 7 and the radiation electrode 2 so as to be separated fromeach other, as in the second preferred embodiment, the degree ofcoupling between the magnetic field electrode 7 and the radiationelectrode 2 can be precisely adjusted. The degree of coupling betweenthe magnetic field electrode 7 and the radiation electrode 2 isincreased as a width W′ is increased and is decreased as a separation L′becomes is increased, as illustrated in FIG. 6.

Furthermore, in the antenna 30, portions of the radiation electrode 2 inthe vicinity of the center of the radiation electrode 2 in thelongitudinal direction preferably protrude toward the opening 3 andconcave portions 35 are preferably provided. The size of the antenna 30can be reduced by changing the shape of the portions of the radiationelectrode 2 in this manner, while the length of the radiation electrode2 in the longitudinal direction remains substantially fixed. The antenna30 according to the second preferred embodiment preferably has a size ofabout 60 mm in the longitudinal direction, about 40 mm in the widthdirection, and a thickness of about 3 mm, for example.

Third Preferred Embodiment

An antenna 40 according to a third preferred embodiment of the presentinvention is illustrated in FIG. 7. The antenna 40 differs from that ofthe second preferred embodiment in that a ground electrode 41 isarranged on another main surface 12 of the insulator board 1 and theremaining structure thereof is substantially the same as that of thesecond preferred embodiment.

In the first preferred embodiment and the second preferred embodiment,the radiation electrode 2 operates as an antenna due to the potentialdifference that is generated between the radiation electrode 2 and themetal article to which the antenna 20 or 30 is attached. The metalarticle functions as a ground electrode for the radiation electrode 2and, since the radiation electrode 2 and the ground electrode arearranged so as to be insulated from each other, a capacitance (C1, referto FIG. 4) is generated therebetween. This capacitance affects thefrequency of transmission/reception signals that can be transmitted andreceived by the antenna. That is, there is a problem in that, if thecapacitance between the radiation electrode 2 and the ground electrodefluctuates, the frequency of signals that can be transmitted andreceived by the antenna also fluctuates and communication becomesunstable. Furthermore, examples of causes of the changes to thecapacitance between the radiation electrode 2 and the metal articlefunctioning as a ground electrode include variations in the thickness ofthe adhesive used to connect the insulator board 1 to the metal articleand there being a gap between the insulator board 1 and the metalarticle created when adhering the insulator board 1 to the metalarticle.

In order to solve this problem, in the antenna 40 according to the thirdpreferred embodiment, the ground electrode 41 is arranged on the othermain surface 12 of the insulator board 1. With this structure, asillustrated in the equivalent circuit in FIG. 8, a capacitance C2between the radiation electrode 2 and the ground electrode 41 in thethickness direction of the insulator board 1 can be determined andfluctuations of the frequency of signals that can be transmitted andreceived by the antenna 40 are effectively prevented by preventingfluctuations of this capacitance. In addition, in the case where a backsurface electrode provided on a glass epoxy board or other suitableboard formed by injection molding of a resin is preferably used for theground electrode, as in the first preferred embodiment, the metal foilused for the ground electrode can be formed by being simultaneouslyarranged separate from the metal foil of the radiation electrode 2.

The equivalent circuit illustrated in FIG. 8, similar to FIG. 4, is anequivalent circuit of a wireless IC device in which the wireless IC chip51 (refer to FIG. 11), which will be described below, is preferablyconnected to the feeder portion 10 defined by ends 8 and 9.

Fourth Preferred Embodiment

FIGS. 9A and 9B illustrate a wireless IC device 50 according to a fourthpreferred embodiment of the present invention, the wireless IC device 50preferably including the antenna 30. In the wireless IC device 50, thewireless IC chip 51 is arranged on the feeder portion 10. The wirelessIC chip 51 preferably includes a clock circuit, a logic circuit, amemory circuit and other suitable circuits and stores necessaryinformation therein. The wireless IC chip 51 is preferably provided withinput/output terminal electrodes 52 and 52 and mounting terminalelectrodes 53 and 53 on the back surface thereof, as illustrated in FIG.11. The input/output terminal electrodes 52 and 52 are preferablyelectrically connected to the feeder portion 10 defined by the ends 8and 9 of the line-shaped electrodes 5 and 6 through metal bumps, forexample. In addition, Au, solder, or other suitable material, forexample, can preferably be used as the material of the metal bumps.

The operation of the wireless IC device 50 according to the fourthpreferred embodiment will now be described. A transmission signal, whichhas a predetermined frequency and originates from the wireless IC chip51, is transmitted to outside the wireless IC device 50 through themagnetic field electrode 7 and the radiation electrode 2. Furthermore, asignal is received from a reader/writer, which is not illustrated,through the magnetic field electrode 7 and the radiation electrode 2 andis supplied to the wireless IC chip 51. Accordingly, in the wireless ICdevice 50, the wireless IC chip operates due to the signal received bythe magnetic field electrode 7 and the radiation electrode 2 and aresponse signal from the wireless IC chip 51 is radiated to the outsidefrom the magnetic field electrode 7 and the radiation electrode 2.

In order to perform impedance matching between the wireless IC chip 51,and the magnetic field electrode 7 and the radiation electrode 2, animpedance-matching circuit may preferably be provided between the feederportion 10 and the magnetic field electrode 7. Furthermore, when thewireless IC device 50 is manufactured by injection molding of a resin,for example, the wireless IC chip 51 is preferably arranged at theapproximate center of the wireless IC device 50 in the thicknessdirection and, as a result, the wireless IC chip 51 can be preventedfrom being damaged when the wireless IC device 50 is subject to animpact or when a mechanical stress is applied to the wireless IC device50 due to bending or other force.

Fifth Preferred Embodiment

FIGS. 12A and 12B illustrates a wireless IC device 60 according to afifth preferred embodiment of the present invention, the wireless ICdevice 60 includes the antenna 30. The wireless IC device 60 preferablyincludes the wireless IC chip 51, an electromagnetic coupling module 67including a feeder circuit board 65 on which the wireless IC chip 51 ismounted, the magnetic field electrode 7, and the radiation electrode 2.

The fifth preferred embodiment differs from the fourth preferredembodiment in that the feeder circuit board 65 is provided. The feedercircuit board 65 preferably includes a feeder circuit 66 (described indetail below with reference to FIG. 15) including a matching circuit,which includes inductance elements L1 and L2 having different inductancevalues and being inversely magnetically coupled (represented by mutualinductance M), as illustrated by the equivalent circuit in FIG. 13. Thefeeder circuit 66 attempts to match the impedance of the wireless ICchip 51 and the impedance of the magnetic field electrode 7 and theradiation electrode 2.

Therefore, the feeder circuit 66 transfers a transmission signal havinga predetermined frequency and originating from the wireless IC chip 51to the radiation electrode 2 through the magnetic field electrode 7, andsupplies a signal received by the radiation electrode 2 and the magneticfield electrode 7 to the wireless IC chip 51. Accordingly, in thewireless IC device 60, the wireless IC chip 51 operates due to thesignal received by the radiation electrode 2 and the magnetic fieldelectrode 7 and a response signal from the wireless IC chip 51 isradiated to the outside from the magnetic field electrode 7 and theradiation electrode 2.

Next, the structure of the feeder circuit board 65 will be describedwith reference to FIG. 14 and FIG. 15. As illustrated in FIG. 14,preferably, the input/output terminal electrodes of the wireless IC chip51 are connected to feeder terminal electrodes 142 a and 142 b providedon the feeder circuit board 65 and the mounting terminal electrodes ofthe wireless IC chip 51 are connected to mounting terminal electrodes143 a and 143 b through metal bumps, for example.

As illustrated in FIG. 15, the feeder circuit board 65 is formed bystacking on top of one another, pressure bonding together and bakingceramic sheets 141 a to 141 h, which are preferably made of a dielectricor magnetic material, for example. However, the insulating layers of thefeeder circuit board 65 are not limited to being ceramic sheets, and,for example, may be sheets made of a resin, such as a thermosettingresin or a thermoplastic resin such as a liquid crystal polymer. Thefeeder terminal electrodes 142 a and 142 b, the mounting terminalelectrodes 143 a and 143 b, and via hole conductors 144 a, 144 b, 145 aand 145 b are preferably formed on and through the uppermost sheet 141a. Wiring electrodes 146 a and 146 b, which respectively define theinductance elements L1 and L2, and via hole conductors 147 a, 147 b, 148a and 148 b are preferably formed on and though the second to eighthsheets 141 b to 141 h, as necessary.

By stacking the sheets 141 a to 141 h on top of one another, theinductance element L1, in which the wiring electrodes 146 a areconnected to one another in a helical shape by the via hole conductors147 a, is formed and the inductance element L2, in which the wiringelectrodes 146 b are connected to one another in a helical shape by thevia hole conductors 147 b, is formed. In addition, capacitances areformed between wires of the wiring electrodes 146 a and 146 b.

An end portion 146 a-1 of the wiring electrode 146 a on the sheet 141 bis connected to the feeder terminal electrode 142 a through the via holeconductor 145 a and an end portion 146 a-2 of the wiring electrode 146 aon the sheet 141 h is connected to the feeder terminal electrode 142 bthrough the via hole conductors 148 a and 145 b. An end portion 146 b-1of the wiring electrode 146 b on the sheet 141 b is connected to thefeeder terminal electrode 142 b through the via hole conductor 144 b andan end portion 146 b-2 of the wiring electrode 146 b on the sheet 141 his connected to the feeder terminal electrode 142 a through the via holeconductors 148 b and 144 a.

In the above-described feeder circuit 66, the inductance elements L1 andL2 are preferably wound in opposite directions to each other and,therefore, the magnetic fields generated by the inductance elements L1and L2 cancel each other out. Since the magnetic fields cancel eachother out, it is necessary that the wiring electrodes 146 a and 146 bhave a certain length in order to obtain the desired inductance values.Thus, the Q value is reduced and, therefore, the resonancecharacteristic is relatively flat and the band is widened in thevicinity of the resonant frequency.

The inductance elements L1 and L2 are formed at different positions inthe left-right direction when the feeder circuit board 65 is viewed inplan. In addition, the magnetic fields generated by the inductanceelements L1 and L2 are in opposite directions to each other. Thus, whenthe feeder circuit is coupled with the feeder portion 10 defined by theline-shaped electrodes 5 and 6, a current can be generated in themagnetic field electrode 7 due to currents being excited in oppositedirections in the line-shaped electrodes 5 and 6, and the radiationelectrode 2 operates as a patch antenna due to the potential differencecaused by this current. By including a matching circuit in the feedercircuit board 65, as in the fifth preferred embodiment, a space for amatching circuit which previously had to be provided separately on theinsulator board 1 can be omitted and a reduction in the size of thewireless IC device can be achieved due to the reduction in size of theantenna. Furthermore, since the matching circuit is built into the board65, fluctuations in the characteristics of the matching circuit due tothe influence of external articles are prevented and deterioration ofcommunication quality is prevented. In addition, in the fifth preferredembodiment, the wireless IC chip 51 of the electromagnetic couplingmodule 67 is preferably arranged at the approximate center of thewireless IC device 60 in the thickness direction and, thereby, thewireless IC chip 51 is protected from being damaged and the mechanicalstrength of the wireless IC device is improved.

With the structure of the wireless IC device 60 illustrated in FIGS. 12Aand 12B, an RFID was manufactured that had a communication frequency ofabout 950 MHz, and when this RFID was arranged on an Al metal plate andthe radiation characteristics thereof were investigated, a radiationgain of about −0.6 MHz was obtained at about 950 MHz. Furthermore, inthis experiment, the distance from the Al metal plate to the radiationelectrode 2 was about 3 mm and the radiation characteristic was improvedto about +1 dB by increasing this distance be about 4 mm, for example.

Sixth Preferred Embodiment

An antenna 70 according to a sixth preferred embodiment of the presentinvention is illustrated in FIGS. 16A to 16C. In the antenna 70, anopening 103 and a slit 104 are preferably provided in a radiationelectrode 102 provided on the one main surface 11 of the insulator board1, the slit 104 extending from the opening 103 to an edge portion 103 aof the radiation electrode 102. One end portion 102 a that projects intothe opening 103 opposes another end portion 102 b and the one endportion 102 a and the other end portion 102 b preferably define a feederportion. In the sixth preferred embodiment, a magnetic field electrode107 is provided in an area surrounding the opening 103, which includesthe one end portion 102 a and the other end portion 102 b. That is, inthe sixth preferred embodiment, in contrast to the first to fifthpreferred embodiments, the radiation electrode 102 has a loop shape thatis opened by the slit 104, and therefore, a current is concentrated inan inner peripheral edge portion (area surrounding the opening 103) ofthe radiation electrode 102. This inner peripheral edge portionfunctions as the magnetic field electrode 107. In this case (similarlyto the following preferred embodiments and modifications), the radiationelectrode and the magnetic field electrode are formed in an integratedmanner.

In the sixth preferred embodiment, a signal is transferred to themagnetic field electrode 107 from the feeder portion and the signal isthen radiated to the outside from the radiation electrode 102, which isintegrated with the magnetic field electrode 107. In this manner, sincethe magnetic field electrode 107 and the radiation electrode 102 areintegrated with each other, a signal can be transmitted to the outsidefrom the feeder portion with the characteristics thereof (for example,wide-band frequency characteristics) remaining substantially unchanged.This is also the case when a signal is received.

As illustrated in FIG. 16C, the antenna 70 is preferably arranged on ametal plate 75, the metal plate 75 functions as a ground electrode, theradiation electrode 102 functions as a patch antenna, and communicationis performed. The operation and operational advantages of the antenna 70are substantially the same as those of the first preferred embodiment.In particular, the slit 104 is preferably provided in the radiationelectrode 102 and thereby the radiation electrode 102 and the magneticfield electrode 107 can be formed in an integrated manner and an antennais obtained that has a very simple structure. In addition, the metalplate 75 is not necessarily required, as in the first preferredembodiment.

Seventh Preferred Embodiment

An antenna 80 according to a seventh preferred embodiment of the presentinvention is illustrated in FIG. 17. The antenna 80 differs from that ofthe sixth preferred embodiment in that a ground electrode 85 is arrangedon the other main surface 12 of the insulator board 1 and the remainderof the structure thereof is substantially the same as that of the sixthpreferred embodiment. The operational advantage of providing the groundelectrode 85 was described in the third preferred embodiment.

Modifications of Sixth Preferred Embodiment

First, second, third and fourth modifications of the sixth preferredembodiment are illustrated in FIGS. 18A to 18D. In the firstmodification (antenna 70A) illustrated in FIG. 18A, preferably, theopening 103 of the radiation electrode 102 has a comparatively largearea and the one end portion 102 a and the other end portion 102 b arearranged in an edge portion of the radiation electrode 102. In thesecond modification (antenna 70B) illustrated in FIG. 18B, preferably,the one end portion 102 a and the other end portion 102 b, which definethe magnetic field electrode 107, are arranged so as to protrude intothe opening 103. In the third modification (antenna 70C) illustrated inFIG. 18C, preferably, the one end portion 102 a and the other endportion 102 b, which define the magnetic field electrode 107, opposeeach other with the slit 104 therebetween. In the fourth modification(antenna 70D) illustrated in FIG. 18D, the opening 103 preferably has acircular shape, for example, but may instead have an elliptical shape.

The operation and operational advantages of the antennas 70A to 70Ddescribed in the first to fourth modifications are substantially thesame as those of the sixth preferred embodiment. In particular, byarranging components of the feeder portion (102 a and 102 b) so as toface each other in the width direction of the insulator board 1, as inthe antennas 70A and 70B, the wireless IC chip or electromagneticcoupling module (feeder circuit board) mounted on the feeder portion canbe securely fixed in place. That is, the rectangular insulator board 1readily bends in the longitudinal direction but does not readily bend inthe width direction. Even when the insulator board 1 is bent in thelongitudinal direction, the wireless IC chip or the feeder circuit boardis coupled to the feeder portion in the width direction and, therefore,is unlikely to be disconnected from the feeder portion so as tosignificantly improve reliability. These advantages are similarlyprovided by the sixth and seventh preferred embodiments.

Eighth Preferred Embodiment

An antenna 90 according to an eighth preferred embodiment of the presentinvention is illustrated in FIG. 19A. In the antenna 90, a conductor ispreferably arranged so as to extend in the longitudinal direction fromthe front surface of the insulator board 1 to the back surface thereofvia an edge surface. Preferably, in the front surface portion of thisconductor, functioning as the radiation electrode 102, the opening 103is provided, which includes the one end portion 102 a and the other endportion 102 b, and the magnetic field electrode 107 is provided in anarea surrounding the opening 103. The back surface portion of theconductor functions as a counter electrode 105 and the counter electrode105 is coupled with the radiation electrode 102 through the capacitanceC3 of an end portion thereof. Furthermore, an inductance L5 shown inFIG. 19B is formed in a portion that directly connects the ends of theradiation electrode 102 and the counter electrode 105.

In the eighth preferred embodiment, a potential difference generated inthe magnetic field electrode 107 is transferred to the radiationelectrode 102 and the radiation electrode 102 operates as a patchantenna due to the potential difference between the radiation electrode102 and the counter electrode 105. The capacitance C3 formed between theradiation electrode 102 and the counter electrode 105 is comparativelysmall and the frequency of signals that can be transmitted and receivedare determined by this capacitance C3.

In addition, as illustrated in FIG. 19B, a ground electrode (metalarticle) 43 may preferably be arranged so as to oppose the counterelectrode 105 on the back surface side of the antenna 90. The counterelectrode 105 and the ground electrode are preferably coupled with eachother through a comparatively large capacitance C5 and the groundelectrode 43 is excited through the counter electrode 105. In addition,the capacitance C5 may be infinitely large, that is to say, the groundelectrode 43 may be in direct conductive contact with the counterelectrode 105.

Ninth Preferred Embodiment

An antenna 100 according to a ninth preferred embodiment of the presentinvention is illustrated in FIG. 20A. In the antenna 100, preferably,the counter electrode 105 and the radiation electrode 102 of the antenna90 according to the eighth preferred embodiment are isolated from eachother and the radiation electrode 102 and the counter electrode 105 arecoupled with each other through capacitances C3 and C4 formed at endportions thereof. The remainder of the structure is substantially thesame as that of the antenna 90.

Also in the ninth preferred embodiment, a potential difference generatedin the magnetic field electrode 107 is transferred to the radiationelectrode 102 and the radiation electrode 102 operates as a patchantenna due to the potential difference between the radiation electrode102 and the counter electrode 105. The capacitances C3 and C4 formedbetween the radiation electrode 102 and the counter electrode 105 arecomparatively small and the frequencies at which transmission andreception can be performed are determined by these capacitances C3 andC4.

Furthermore, as illustrated in FIG. 20B, preferably, the groundelectrode (metal article) 43 may be arranged so as to oppose the counterelectrode 105 on the back surface side of the antenna 100 and the twoelectrodes may be coupled with each other through the capacitance C5 ormay be in direct conductive contact with each other.

Tenth Preferred Embodiment

An antenna 110 according to a tenth preferred embodiment of the presentinvention is illustrated in FIG. 21A. In the antenna 110, the counterelectrode 105 of the antenna 90 according to the eighth preferredembodiment is preferably reduced in length. The remainder of thestructure is substantially the same as that of the antenna 90.

In the tenth preferred embodiment, as illustrated in FIG. 21B, acomparatively small capacitance C6 is formed between an end portion ofthe radiation electrode 102 and the ground electrode (metal article) 43and a comparatively large capacitance C5 is formed between the counterelectrode 105 and the ground electrode 43. Therefore, the groundelectrode 43, which is coupled with the radiation electrode 102 and thecounter electrode 105 through the capacitances C6 and C5, is excited.Frequencies at which transmission and reception can be performed aredetermined by the small capacitance C6. Therefore, the feature that thecounter electrode 105 and the ground electrode 43 may be in directconductive contact with each other is substantially the same as in theeighth preferred embodiment and the ninth preferred embodiment.

In the antenna according to preferred embodiments of the presentinvention, a magnetic field electrode is provided between a radiationelectrode and a feeder portion. That is, the radiation electrode and themagnetic field electrode are preferably integral with each other. Withthis structure, a feeder pin and a side surface electrode, which werenecessary in patch antennas of the background art, are no longerrequired, a process of manufacturing the antenna is simplified, and thereliability of a connection between the radiation electrode and thefeeder portion is significantly improved.

A counter electrode and/or a ground electrode may preferably be arrangedso as to oppose the radiation electrode, and the ground electrode mayalso be arranged so as to oppose the counter electrode. It is preferablethat the radiation electrode and the ground electrode are coupled witheach other through a capacitance. In addition, the radiation electrodeand the counter electrode may be in direct conductive contact with eachother through end portions thereof. The counter electrode and the groundelectrode may be coupled with each other through a capacitance or may bein direct conductive contact with each other.

Furthermore, in the antenna according to preferred embodiments of thepresent invention, preferably, an opening is provided in the radiationelectrode and the magnetic field electrode is connected to an innerperipheral portion of the opening of the radiation electrode. With thisstructure, the magnetic field electrode can be arranged inside theradiation electrode and the antenna can be reduced in size.

In addition, in the antenna according to preferred embodiments of thepresent invention, the magnetic field electrode is preferably defined bya plurality of line-shaped electrodes that are provided on one mainsurface of an insulator board, first ends of the plurality ofline-shaped electrodes being connected to the radiation electrode,second ends of the plurality of line-shaped electrodes being arranged soas to oppose each other, and a feeder portion being defined by thesecond ends. With this structure, a current is generated in the magneticfield electrode due to a transmission/reception signal. Then, resonanceis generated due to the outer peripheral shape of the radiationelectrode and the radiation electrode operates as an antenna due to thepotential difference generated by the current.

Furthermore, in the antenna according to preferred embodiments of thepresent invention, preferably, the first ends of the plurality ofline-shaped electrodes may be connected to each other and may beconnected to the radiation electrode through this connection portion.

In addition, in the antenna according to preferred embodiments of thepresent invention, it is preferable that the second ends of theplurality of line-shaped electrodes be arranged so as to face each otherin the width direction of the insulator board. When the wireless IC chipor the feeder circuit board is coupled with the second ends, since theinsulator board does not readily bend in the width direction, there isno risk of the wireless IC chip or the feeder circuit board separatingfrom the insulator board.

In the antenna according to preferred embodiments of the presentinvention, an opening and a slit may preferably be provided in theradiation electrode, the slit extending from the opening to an edgeportion of the radiation electrode, and the magnetic field electrode mayarranged in an area surrounding the slit. Thereby, the structure of theantenna can be simplified.

In addition, in the antenna according to preferred embodiments of thepresent invention, it is preferable that the radiation electrode bedefined by a planar electrode having a longitudinal direction and awidth direction and that the electrode length in the longitudinaldirection correspond to an electrical length of about ½ the wavelengthof the frequency band of signals to be transmitted and received. Withthis structure, the radiation electrode can operate as an antenna thatresonates at about ½ the wavelength.

Furthermore, in the antenna according to preferred embodiments of thepresent invention, it is preferable that an insulator material bearranged so as to cover the radiation electrode on the one main surfaceof the insulator board and, thereby, the environmental resistance of theradiation electrode can be improved. It is preferable that the thicknessof the insulator material be less than the thickness of the insulatorboard.

In addition, in the antenna according to preferred embodiments of thepresent invention, the insulator board and/or the insulator material maypreferably be formed by injection molding of a resin, for example. Theradiation electrode can preferably be formed in an integrated manner soas to be covered by the insulator material and, thereby, the antenna canbe formed in a simple manner.

In addition, antennas and wireless IC devices according to preferredembodiments of the present invention are not limited to those of theabove-described preferred embodiments and can be modified in variousways within the scope of the present invention.

In particular, in the above-described preferred embodiments, aninsulator material was arranged so as to cover the radiation electrodeon the one main surface side of the insulator board, but the insulatormaterial may be omitted depending on the usage environment of theantenna or wireless IC device. In addition, main surfaces of the antennaor wireless IC device according to the above-described preferredembodiments had a rectangular shape but they are not limited to thisshape and may, for example, have a circular or oval shape.

As has been described above, preferred embodiments of the presentinvention is useful in antennas and wireless IC devices and isparticularly preferable in that the manufacturing process is simple andthe probability of a poor connection occurring between a feeder portionand a radiation electrode is very low.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. An antenna comprising: an insulator board; a radiation electrodeprovided on a first main surface of the insulator board; a magneticfield electrode connected to the radiation electrode; and a feederportion connected to the magnetic field electrode; wherein the radiationelectrode is arranged in an area surrounding the magnetic fieldelectrode.
 2. An antenna comprising: an insulator board; a radiationelectrode provided on a first main surface of the insulator board; aground electrode arranged on a second main surface of the insulatorboard so as to oppose the radiation electrode; a magnetic fieldelectrode connected to the radiation electrode; and a feeder portionconnected to the magnetic field electrode.
 3. The antenna according toclaim 2, wherein the radiation electrode and the ground electrode arecoupled with each other through a capacitance.
 4. An antenna comprising:an insulator board; a radiation electrode provided on a first mainsurface of an insulator board; a counter electrode arranged on a secondmain surface of the insulator board so as to oppose the radiationelectrode, the counter electrode being coupled with the radiationelectrode through a capacitance; a magnetic field electrode connected tothe radiation electrode; and a feeder portion connected to the magneticfield electrode.
 5. The antenna according to claim 4, further comprisinga ground electrode arranged so as to oppose the counter electrode. 6.The antenna according to claim 4, wherein the radiation electrode andthe counter electrode are in direct conductive contact with each otherthrough end portions thereof.
 7. The antenna according to claim 5,wherein the counter electrode and the ground electrode are coupled witheach other through a capacitance.
 8. The antenna according to claim 5,wherein the counter electrode and the ground electrode are in directconductive contact with each other.
 9. The antenna according to claim 1,wherein an opening is provided in the radiation electrode and themagnetic field electrode is connected to an inner peripheral portion ofthe opening of the radiation electrode.
 10. The antenna according toclaim 1, wherein the magnetic field electrode is defined by a pluralityof line-shaped electrodes provided on the first main surface of theinsulator board, first ends of the plurality of line-shaped electrodesare connected to the radiation electrode and second ends of theplurality of line-shaped electrodes are arranged so as to face eachother, and the feeder portion is defined by the second ends of theplurality of line-shaped electrodes.
 11. The antenna according to claim10, wherein the first ends of the plurality of line-shaped electrodesare connected to each other at a connection point and are connected tothe radiation electrode through the connection point.
 12. The antennaaccording to claim 1, wherein an opening and a slit are provided in theradiation electrode, the slit extending from the opening to an edgeportion of the radiation electrode, and the magnetic field electrode isprovided in an area surrounding the opening.
 13. The antenna accordingto claim 1, wherein the feeder portion is arranged such that componentsof the feeder portion face each other in a width direction of theinsulator board.
 14. The antenna according to claim 1, wherein theradiation electrode is defined by a planar electrode having alongitudinal direction and a width direction, and an electrode length ofthe planar electrode in the longitudinal direction corresponds to anelectrical length of substantially ½ a wavelength of a frequency band ofsignals to be transmitted and received.
 15. The antenna according toclaim 1, wherein an insulator material is arranged so as to cover theradiation electrode on the first main surface of the insulator board.16. The antenna according to claim 1, wherein a thickness of theinsulator material is less than a thickness of the insulator board. 17.The antenna according to claim 15, wherein at least one of the insulatorboard or the insulator material is made of an injection molded resin.18. A wireless IC device comprising: the antenna according to claim 1;and a wireless IC; wherein the wireless IC is arranged so as to becoupled with the feeder portion.
 19. A wireless IC device comprising:the antenna according to claim 1; a wireless IC; an electromagneticcoupling module coupled with the wireless IC and including a feedercircuit board that includes a feeder circuit including at least one of aresonance circuit or a matching circuit that includes an inductanceelement; wherein the electromagnetic coupling module is arranged so asto be coupled with the feeder portion.